This invention relates to an improved movable tarpaulin cover system for open-top truck bodies and more particularly relates to an improvement in the construction of intermediate bows used in such a system.
Movable tarpaulin cover systems for truck boxes or trailers of the type including a floor, front wall and a pair of upright side walls and/or flatbed trailers are known in the prior art. See for example Cramaro U.S. Pat. No. 4,189,178 issued Feb. 19, 1980. In such systems, one end of the tarpaulin to cover the truck body is anchored to the front wall. A plurality of intermediate support bows extend in parallel fashion from side to side transversely across a truck body, the bows being secured to the tarpaulin at spaced locations. The ends of the intermediate bows are slidably secured on each side of the truck body to movable cable means for longitudinal movement with respect to the truck body. A lead bow extends parallel to the intermediate bows from side to side transversely across a truck body and is secured to the tarpaulin. The ends of this bow are secured on each side to the movable cable means to move with them longitudinally with respect to the truck body. When the cables are moved in one direction, the lead bow and free end of the tarpaulin are drawn longitudinally to the back end of the truck body thereby pulling the tarpaulin. The intermediate bows are pulled rearwardly with the tarpaulin to varying distances, depending upon where they are secured to the tarpaulin rearwardly as required to cover the truck body. When the cable is moved in the opposite direction, the lead bow, intermediate bows and tarpaulin are retracted to the front end of the truck body to open position.
In the Cramaro system described and illustrated in the aforementioned U.S. patent, a pair of cables are provided, one on each side of the truck body or box, each cable providing one of a pair of horizontal reaches of cable extending along parallel to and above each of the upper edges of the box. The two cables are simultaneously winched for movement.
Despite the widespread use of this Cramaro tarpaulin system in North America today, a significant problem exists with it in that it tends to jam, during movement of the cables to either open or closed the tarpaulin over the truck body top. For proper operation, the cable must slide freely through the ends of the intermediate bows. In this regard to each end of the intermediate bows is secured a cylindrical sleeve through which the corresponding cable passes. What has tended to occur has been that one end or the other of an intermediate bow during movement of the tarpaulin to open or closed position, has moved either ahead of or behind the other end of the intermediate bow causing the cable to be crimped within the sleeve and preventing further relative movement of that cable through that sleeve. This causes the cable to drag this intermediate bow with it until further motion of that bow is prevented by the tarpaulin (when closing) or intermediate bows bunched at the front end of the truck body (when opening). At this point further motion of the cables in that direction is arrested and cannot be continued until the cable is uncrimped within the sleeve (usually by lateral realignment of that intermediate bow) and freed to slide again within that sleeve.
Because conventionally the bows arched upwardly across the truck box to support the tarpaulin in a raised position, it is not a solution merely to provide a sleeve of larger diameter. This would result in the arch of the bow falling forwardly or rearwardly since the enlarged sleeves would be supported too loosely on the cables.
It is an objection of the present invention to provide an improved tarpaulin cover system of the type in question which does not seize up so readily during operation.